The only successful known method of terminating high frequency cardiac arrhythmias is cardioversion also known as defibrillation. In defibrillation the heart is reset by a single high voltage and high current electric shock of a high energy which is also designated as the conventional cardioversion or defibrillation energy here. In extra-corporal defibrillation, the voltage of such an electric shock typically amounts to about 1000 Volts, its current to about 30 Amperes, and the conventional or state of art defibrillating energy to about 360 Joules. For intracardiac defibrillation, the conventional or state of art defibrillating energy is about 5 to 20 Joules. In both cases, the electric field during the electric shock is about 6 V/cm. A discharge of a defibrillator in a conscious patient is painful and extremely unpleasant. It also has potential tissue damaging effects.
Antitachycardia pacing (ATP) is a much more gentle known method. It is not painful, because the energy of its pacing pulses is several orders of magnitude less than the conventional cardioversion or defibrillation energy. ATP, however, is only successful against low frequency arrhythmias (frequency not higher than 4 Hz). Its success rate decreases fast with increasing frequency of the arrhythmia, and high frequency cardiac arrhythmias (frequencies larger 4 Hz), and atrial fibrillation (AF) and ventricular fibrillation (VF) cannot be terminated by ATP.
Allessie M, et al., Regional control of atrial fibrillation by rapid pacing in conscious dogs. Circulation. 1991; 84:1689-1697 have tried to entrain AF, i.e. to control it by pacing pulses at a high frequency. They were successful only locally, i.e. in a small vicinity (several cm) of the pacing electrode; outside of this vicinity AF is not entrained.
An obvious solution to this problem would be to pace AF from so many sites, i.e. with so many pacing electrodes, that they cover the atrium dense enough. But many implanted pacing electrodes and their connecting wires would severely damage a contracting heart.
U.S. Pat. No. 4,996,984 issued to Sweeney discloses a method of defibrillating a mammal in need of defibrillation. This known method comprises first determining the mammal's fibrillation cycle length; and then administering to said mammal two bursts of electrical current delivered sequentially to said mammal. The current of each of the burst is from about 4 Amperes to about 10 Amperes; the voltage of each burst is from about 200 Volts to about 300 Volts; the duration of each burst is from about 8 milliseconds to about 15 milliseconds; and the timing between the two bursts is adjusted to about 75% of the mammal's fibrillation cycle length. The energy of each of the bursts which are administered within the body of the mammal is reported to be as low as 3 Joules. The fibrillation cycle length of a fibrillating heart is obtained using fast Fourier transformation, for example.
U.S. Pat. No. 7,418,293 issued to Sweeney discloses further reducing the electric energy required for terminating a fibrillation event as compared to a single pulse used for defibrillation by means of multiple pulse defibrillation. The reported minimum energy per pulse in multiple pulse defibrillation is about a quarter of the energy required for defibrillation by means of a single pulse.
U.S. Pat. No. 7,006,867 issued to Kroll discloses a method for overdrive pacing a patient's heart using an implantable cardiac stimulation device connected to the heart. The known method comprises disposing a plurality of leads within an atrium of the heart, sensing atrial activity through at least one of the plurality of leads, determining an overdrive pacing rate based in part on the sensed atrial activity, and delivering atrial pacing pulses to the atrium through at least one of the plurality of leads at the overdrive pacing rate. A first one of the plurality of leads may be coupled to the interatrial septum of the atrium, a second one of the plurality of leads may be coupled to the sinus node of the atrium, and a third one of the plurality of leads may be coupled to the left atrium through the coronary sinus/great vein of the patient's heart. The known method includes multiple site sensing and/or multiple site pacing. In one embodiment, the delivering step comprises delivering the atrial pacing pulses in a staggered manner, with a first pulse delivered to a first one of the plurality of leads and a second pulse delivered to a second one of the plurality of leads, and with a predetermined time delay defined between delivery of the first and second pulses.
An apparatus for terminating high frequency arrhythmias and AF is needed that operates at an energy level much lower than that of conventional cardioversion/defibrillation and that is nevertheless able to terminate arrhythmias that ATP cannot terminate. It would be highly appreciated if the energy level could remain below the pain threshold.